"Thanks for the feedback! Votes cast by those with less than 15 reputation are recorded, but do not change the publicly displayed post score."
Votes "cast by" simply means the votes from or votes given by, in this case, "those with less than 15 reputation". Possibly originates from ancient Greece - "the Ancient Greeks used pebbles to cast their votes – apparently depositing a small stone into one of two urns to mark their choice. After the vote had taken place, the contents of the urns were emptied and counted" http://blog.oxforddictionaries.com/2015/05/vocabulary-voting-election-etymology/